Since we always had the problem that our cats wanted to play with the christmas balls and then they broke, I decided to print some myself.
I printed them without infill and 0.12mm layer height. At the beginning of the sphere and at the top I set the layer height to 0.08mm so that the layers are not so visible. I printed them with the top side on the printing plate.
The small hook can simply be pushed into the top of the ball, which then snaps into place but can be removed again if desired.